Global emissions of carbon dioxide dropped by 1.3% in 2009 compared with the previous year, largely due to the effects of the economic crisis and an overall fall in GDP, according to an international team of scientists.

The drop is smaller than the 2.8% fall predicted by many experts for 2009, however, because the reductions in carbon emissions per unit of GDP - a measure of efficiency called the carbon intensity - was smaller than expected in many emerging economies.

The results are part of the annual carbon budget update by the Global Carbon Project (GCP), an international group of climate scientists and analysts that collates emissions data to help policymakers. The project totalled the carbon emissions due to use of fossil fuels in power stations, cement manufacture and changes in land use, such as deforestation.

Despite the 1.3% overall drop, the 2009 global fossil fuel emissions - 30.8bn tons of CO2 - were the second highest in human history, just below the all-time high of 2008.

The small overall decrease in global emissions masks some big regional shifts, according to the report published today in Nature Geoscience. Because the global financial crisis has mainly affected developed nations, this is where emissions dropped by the largest amounts: in the US by 6.9%, the UK by 8.6%, Germany by 7%, Japan by 11.8%, Russia by 8.4% and Australia by 0.4%.

In the emerging markets, however, there were big increases: China rose by 8%, India by 6.2% and South Korea by 1.4%.

"The 2009 drop in CO2 emissions is less than half that anticipated a year ago," said Pierre Friedlingstein, a professor of mathematical modelling of climate systems at the University of Exeter. "This is because the drop in world GDP was less than anticipated and the carbon intensity of world GDP improved by only 0.7% in 2009, well below its long-term average of 1.7% per year."

This relatively poor improvement in carbon intensity was caused by an increased reliance on coal in the emerging economies, Friedlingstein said.

The GCP also found that global CO2 emissions associated with deforestation have dropped by 25% since 2000. This is mainly due to a reduction in tropical deforestation, which is consistent with reports of satellite data over the Brazilian Amazon and Indonesia.

"For the first time, forest expansion in temperate latitudes has overcompensated deforestation emissions and caused a small net sink of CO2 outside the tropics," said Corinne Le Quéré of the University of East Anglia and the British Antarctic Survey. "We could be seeing the first signs of net CO2 sequestration in the forest sector outside the tropics."

If world economies start to recover and grow in 2010 as predicted, however, the 2009 fall in emissions will not continue into the future. "CO2 emissions from fossil fuels are projected to increase by more than 3% in 2010 if economic growth proceeds as expected, approaching the high emissions growth rates observed from 2000 to 2008," said Pep Canadell, a scientist at the Commonwealth Scientific and Industrial Research Organisation in Australia and executive director of GCP.

Despite the 1.3% drop in emissions, atmospheric concentrations of CO2 continued to increase in 2009, reaching a global average of 387.2 parts per million (ppm) at the end of the year. Prior to the industrial revolution, CO2 levels were around 280ppm. They are now rising at 2-3ppm per year and, when other greenhouse gases such as methane are included, the total level in the atmosphere, known as the carbon dioxide equivalent, is closer to 440ppm.

Computer models predict that if emissions continue to rise at the present rate, average temperatures are likely to increase by 4C by 2100.